Scientists at the University of Illinois at Chicago have succeeded for the first time in growing a full-size copy of a human jaw joint complete with bone and cartilage.

The achievement, which was accomplished by coaxing rat stem cells to multiply into the complex jaw structure, may be the forerunner of what eventually could become a new era of designer replacement body parts.

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To make the jaw joint, Mao started with a single population of stem cells isolated from rat bone marrow. Mao and Adel Alhadlaq, a doctoral student, treated the stem cells with growth hormones and other chemicals, causing them to form bone and cartilage. These cells, called mesenchymal stem cells, are found in a number of different tissues and have been induced to make tendons, muscle, teeth, ligaments, cartilage and bone.

They were then inserted into a biocompatible synthetic gel-like substance to hold the cells together. The gel and its cargo of multiplying cells were placed inside a mold shaped like the ball of a human jaw, taken from a human cadaver. In four weeks the cells grew into the shape of the ball that fits into the socket.

The cells grew with a cartilage layer on top and a bone layer on the bottom, the same configuration that occurs in natural jaw joints.